Nowadays esters from fatty acids and ethanol have obtained a huge economic relevance since these esters—known as “biodiesel”—are used as a substitute for LPG (liquid petroleum gas) or alternatively as an adjuvant for conventional fuels. A major reason for this development is that the esters are based on renewable resources: vegetable oils for the fatty acid part of the molecule and ethanol from the fermentation of starch and other carbohydrates for the ester group. The use of biodiesel therefore represents a contribution to sustainable exploitation of nature rather than the consumption of resources which have been created during billions years and cannot be renewed. This is the major reason for which the European Union has decided to require oil companies to add an increasing amount of biodiesel to LPG based on petrochemicals
Commercial processes usually start at present from starch or glucose which are subjected to fermentation to provide an mixture of ethanol and water. For the future other plant biomass sources like cellulose, lignocellulose, hemicelluloses, straw or wood will be useful for the economic production of biofuels like ethanol. A key issue of such process however is to separate the alcohol from the water, since this is a very energy intensive process. For example, a modern motor fuel ethanol plant has a total energy-consumption of 1.1-1.4 MegaJ per liter of ethanol. Even the newest commercial installations are based on a pressure-cascading technique and consume 3.0-4.2 kg of steam for every liter of 96 Vol-% ethanol produced. Earlier distillation systems required 6 kg of steam per liter of ethanol. Unfortunately, the typical transesterification processes do not allow the use of aqueous alcohols in the presence of water hydrolysis becomes a competitive reaction to transesterification. As a matter of fact, according to the state of the art, water is separated out of the transesterification reaction to avoid unwanted side-reactions Thus, it would be highly desirous to develop a process which would avoid any energy-consuming procedure to separate or even reduce the water content in ethanol obtained from fermentation in order to make a transesterification possible, that provides high conversion and selectivity, although conducted under aqueous conditions. The problem underlying the present invention has therefore been to develop such processes in order to reduce costs for the manufacture of biodiesel and to make this important raw material available at lower prices.